Introduce the 'minSize' dataset property for bar controller

Author: adube

docs/charts/bar.md

@@ -77,6 +77,7 @@ Some properties can be specified as an array. If these are set to an array value
 | `hoverBackgroundColor` | `Color/Color[]` | The fill colour of the bars when hovered.
 | `hoverBorderColor` | `Color/Color[]` | The stroke colour of the bars when hovered.
 | `hoverBorderWidth` | `Number/Number[]` | The stroke width of the bars when hovered.
+| `minSize` | `Number` | The minimum size (height for vertical, width for horizontal) in pixels bars should be rendered.
 
 ### borderSkipped
 This setting is used to avoid drawing the bar stroke at the base of the fill. In general, this does not need to be changed except when creating chart types that derive from a bar chart.

src/controllers/controller.bar.js

@@ -382,8 +382,10 @@ module.exports = function(Chart) {
 			var chart = me.chart;
 			var meta = me.getMeta();
 			var scale = me.getValueScale();
+			var isHorizontal = scale.isHorizontal();
 			var datasets = chart.data.datasets;
 			var value = scale.getRightValue(datasets[datasetIndex].data[index]);
+			var minSize = datasets[datasetIndex].minSize;
 			var stacked = scale.options.stacked;
 			var stack = meta.stack;
 			var start = 0;
@@ -410,6 +412,15 @@ module.exports = function(Chart) {
 			head = scale.getPixelForValue(start + value);
 			size = (head - base) / 2;
 
+			if (minSize !== undefined && Math.abs(size) < minSize) {
+				size = minSize;
+				if (value >= 0 && !isHorizontal || value < 0 && isHorizontal) {
+					head = base - minSize;
+				} else {
+					head = base + minSize;
+				}
+			}
+
 			return {
 				size: size,
 				base: base,